Reversible and irreversible magnetization of the Chevrel-phase superconductorPbMo6S8

Magnetic measurements have been carried out on the hot-isostatically-pressed Chevrel-phase superconductor ${\mathrm{PbMo}}_6$ ${\mathrm{S}}_8$ at temperatures from 4.2 K to ${\mathit{T}}_{\mathit{c}}$ and for magnetic fields up to 12 T. The results show that for the ${\mathrm{PbMo}}_6$ ${\mathrm{S}}_8$ compound there is a wide magnetically reversible region, between the irreversibility field ${\mathit{B}}_{\mathrm{}\mathrm{irr}}$ and the upper critical field ${\mathit{B}}_{\mathit{c}2}$, on the isothermal magnetic hysteresis curves. The ${\mathit{B}}_{\mathrm{irr}}$(T) line, i.e., the irreversibility line, was found to obey a power-law expression: ${\mathit{B}}_{\mathrm{irr}}$=${\mathit{B}}^{\mathrm{*}}$(1-T/${\mathit{T}}_{\mathit{c}}$ ${)}^{\mathrm{\alpha }}$ with α≊1.5. Magnetic relaxation measurements revealed that the flux-creep effect in the material studied is substantial and is greater than those observed in conventional metallic alloys, but smaller than in high-temperature superconductors. The existence of the irreversibility line and pronounced flux-creep effect in ${\mathrm{PbMo}}_6$ ${\mathrm{S}}_8$ is attributed to the short coherence length of the material. From the reversible magnetization data, the values of the penetration depth, the coherence length, and the critical fields are obtained together with the Ginzburg-Landau parameter κ. At 4.2 K, the critical current density ${\mathit{J}}_{\mathit{c}}$ is ${10}^9$ A ${\mathrm{m}}^{\mathrm{-}2}$ at zero field, and decreases to 2×${10}^8$ A ${\mathrm{m}}^{\mathrm{-}2}$ at 10 T. Pinning force curves measured at different temperatures obey a Kramer-scaling law of the form: ${\mathit{F}}_{\mathit{p}}$(=${\mathit{J}}_{\mathit{c}}$×B)∝${\mathit{b}}^{1/2}$(1-b${)}^2$, which indicates that the ${\mathit{J}}_{\mathit{c}}$ is limited by one predominant flux-pinning mechanism.